Effek van bewerking op die organiese materiaalinhoud van geselekteerde droëlandgronde in Suid-Afrika

Abstract

The aim of this investigation was to (1) quantify the effect of cultivation on the organic matter content of soils with virgin soils serving as reference; (2) find the relation between cultivation period and the decrease in organic matter and (3) determine whether the decline in organic matter as a result of cultivation differed between ecotopes. Virgin and cultivated topsoils (0 - 200 mm) were sampled at 50 sites which were well distributed throughout the summer rainfall area (24° - 300S; 24° - 30° E). The sites in this area were selected so that a wide range of climatic conditions, soil properties and CUltivation periods was obtained. Cultivation caused a significant decrease in soil organic matter at all sites. This amounted to 10 - 75% in the case of organic C and 5 - 73% in the case of total N. Losses of organic C were consistently larger than total N, with the result that cultivated soils had slightly lower C:N ratios than virgin soils. The rate of organic matter loss was high during the first five years of cultivation. Thereafter the rate decreased until an equilibrium was reached after c. 35 years of cultivation. After this very little or no further loss occurred. The decomposition rate of organic matter because of cultivation in ecotopes of the warm drier areas was higher than in ecotopes of the cooler wetter areas, but the percentage of organic matter lost was larger in the latter areas. © 1994 Taylor & Francis Group, LLC.